Keyless entry systems for vehicles allow users to lock or unlock the doors or trunk of a vehicle without a key. Remote keyless entry systems typically include a pocket-sized fob that includes several pushbuttons that unlock doors or the trunk and perform other functions through encoded RF signals transmitted to a vehicle-installed receiver. Door-mounted keyless entry systems typically include a keypad positioned near the door handle, enabling an authorized user of the vehicle to input a numeric code and thereby gain entry to the vehicle. Such keypads can be used to control other functions, as well.
Some conventional keypads include an array of mechanical switches that are mounted on the keypad and hard-wired to a control module. The keypad typically is fixed to the door panel. As such, the door panel typically includes an opening for receiving the keypad. This opening, if not adequately protected, may permit the surrounding metal panel to corrode and damage the exterior finish. In addition, the keypad itself includes openings for receiving the switches. These openings allow dirt, water and other contaminants to pass into and become trapped within the switch, potentially leading to electrical shorts and other malfunctions.
Other keyless systems use electronic or capacitive solid state switches. Unlike mechanical switches, electronic switches contain no moving parts to break or wear out. However, electronic switches may malfunction when contaminants such as water and debris are present on the touch surface. The contaminants may cause unintended switch actuations. Given that the exterior surface of a vehicle is exposed to a tremendous amount of water, dirt, road spray, and other contaminants, electronic switches have not proven reliable for keyless entry systems. Furthermore, many electronic switches respond to environments with electromagnetic interference (EMI) in unpredictable ways, and may not conform to increasingly rigid electromagnetic compatibility (EMC) standards.